Microwave pulser



March 22, 1960 F. S. COALE MICROWAVE PULSER Filed July 1, 1955 A'ITORNEY United States Patent This invention relates to improved apparatus for generating, pulsed microwave energy, and more particularly, is concerned with apparatus forgener ating extremelyv short high power pulses from a lower power C.-W. or pulsed microwave source.

In order to increase the peak power of a pulse radar system, considerable attention has been given to designing magnetron or klystronoscilla'tors capable of (169' livering' the required peak powers. A number of limiting factors are encountered in both magnetronand klystron, design as higher and higher peak, powers are attempted. The physical bulk of the oscillator tubes is greatly increased by the demand for larger focussing coils, in creased radiation area and enlarged water cooling jackets, shielding against X-rays, and the like. Moreover, there is loss in etficiency because, of increased power supply demands and pulser requirements. The increased ac- 2 output from the source is coupled through a section of. wave guide 14 to a directional coupler indicated generally at 16. The directional coupler includes a primary section ;18 and secondary section 20 of hollow wave guide having a directional, coupling aperture 22 in the common wall between The input end of theprimary wave guidesectio'n 18 is CODPled to the wave guide 14 whilelthe other'end of the wave guide sectionlSis coupled to a non-reflective'termination indicated generally at 24. j

The secondary wave guide section of the coupler 16-jhas the ,respective ends thereof coupled together through a closed conductive loop consisting of an S- shaped section of wave guide 26, a phase shifter indicated generally at 28, a second S-shaped section of wave guide 30, a microwave switch indicated generally at 32:

,- and a U-shaped section of wave guide 34.

The phase shifter 28' is provided to vary the eifective path length around this closed conductive loop and is illustrated as a' type described in copendingS.N. 360,- 327, filed June 8, 1953, in the name of Kiyo Tomiyasu.

f; The phase shifter includes two wave guide sections 36 and 38 having a common narrow wall in which is provided a couplingslot 40. The slot 40 is proportioned to coupled-5 0, of the incident energy. ,Thus, the wave guide sections 36. and 38 with the coupling slot 40.

4 constitutea so-called hybrid coupler. Adjustment of the celerating voltage potentials required are more difficult,

to pulse with the extremely fast pulse duration time desired for high target resolution. v

It is a general object of this invention to avoid the,

foregoing and other limitations in and objections to the prior art practices by the provision of an improved a pulsed microwave source which achieves higher peak powers with shorter pulse times and yet is more eflicient in performance, less complex in design, and more com-, pact in proportion to its output power. 3

Another object of this invention is the provision of apparatus for producing a pulsedhighpeak power microwave output from a Q.-W. source, or a source of output" pulses of long duration compared to the output pulse.

Another object of this invention is to provide apparatus which produces relatively high peak power output pulses froma relatively low power microwave source. j

These and other objects of the invention which will become apparent as the description proceeds are achieved, by the provision of apparatus including a microwave source to which is coupled, through a directional coupler, a wave guide loop forming a continuous closed conductive path. Energy is coupled into the loop in one direction-of propagation from the source, theloop being an. integral number of wavelengths long at the frequency of the source. A gas tube operated switch periodically diverts energy stored in the loop to utilization. means, suchas a radiating'antenna, the energy being dissipated.

.from the loop in an interval of time determined by the propagation time around the loop. v a For a better understanding of the invention reference should be had to the accompanying drawing, wherein:

' Fig. 1 is a plan view, partially in section, of a preferred embodiment of the invention; and V v Fig. 2 isajsectional view taken on the line 2'2 of F 3.

Referring to Fig. l of the drawing, the numeral 10 indicates generally asourc'e of microwave power,'such as a magnetron, orklystron oscillator of medium power. 'Ihesource may operate C. -W. or may be pulsed at a predetermined repetition frequency by a pulser 12. i, The

effective'length of the closed loop path by the phase shifter 28 is accomplished by a pair of short circuiting. plungers 42 and 44 positioned respectively in the end of the wave guide sections 36 and 48. The plungers 42; and 44 are supported by adjusting rods 46 and 48 connected at: one end'to a yoke 50. The yoke 50 is longitudinally positioned by a micrometer screw adjustment operated by a control knob 52, whereby the plungers 42 and 44 are accurately positioned to adjust the amount of .1 phase shift introduced by the phase shifter 28, in the manner taught in the above-mentioned copending application.

Assuming for the moment that the switch 32, to be hereinafter more fully described, couples all the incident energy in the wave guide section 30 to the wave guide section 34, a completely closed conductive loop is protravelling along the wave guide 14. A portion of this vided includingthe secondary wave guide 20 of the direc tional coupler 16. As pointed out and described in co-- pending application S.N. 482,076, filed January 17, 1955, now US. Patent 2,875,415 in the name of Peter 1.; Sferrazza, with the phase shifter 28 set to provide a path length around this loop of an integral number of wavelengths, maximum energy build-up occurs in the closed loop. Assume an incident wave from the source 10 l energy iscoupled into the. wave guide 20 as a coupled wave, and a portion continues down the wave guide 18 as a direct wave to the termination-24. The ratio of coupled energy to direct energy depends on the coupling coefiicient of the ,coupler. around the closed'flloop and, on reaching the coupling aperture 22, is again divided, a portion being coupled to the termination 24 and a portion recirculating around,

the closed loop.

If the phase of the portion recirculating in the loop is such as to add to the coupled wave from the source 10, the'energy in the closed loop in the second cycle will be larger than during the first cycle of energy around the loop. This build-up of energy will continue with each cycle around the loop until the losses within the loop and absorption of energy by the termination 24 exactly' balance the output of the source 10. With substantially zero attenuation around the loop, a steady state condition is reached when the energy coupled to the termination 24 is exactly equal to the energy output of the source Patented Mar-.22, 1960 The coupled Wave travels 3, Undersuchcircumstances, the smaller theamount of coupling, the greater is the total energy stored in the form of a travelling wave around the closed loop, and the more" cycles of the wave in the-closed loopbefore thesteadystate'condition is -reaclied'. This is'so' because: of the relatively small-increment'of energy that is coupled out of the closed'loop foreaeh'cycle. It ha's' been found by keeping the attenuation-around the closedloop very small and by making" the coupling coefiicient of the coupler'16 quite small, energyJbuild-upin'the closed loop of the order of 10 or 1-2'db above=the energy level=of the incident energy from the source'li) canbeacl'iieved.-

According to the principles of the present invention; this energy build up in the closed loop is-iperiodically dimeted out of the loop by the switch '32-"to utilization means, such as a radiator 59. A-preferred switch for thispurpose is illustrated in' Fig; 1 and includes iii-pail of hybrid couplers 60- and 62 having a common -main' wave guide' section 64 coupled between the-waveguide sectio 30 and 34. Secondary'Iwave guideportions;66--and 68? f the: respective hybrid couplers 6t) and 62 inc1ud 90 bends by which they are coupled to a pha'se shifter-"in?- dicated g'enerally at 70. The' other-ends'of- 'the secondary: wave guide portions 66 and 68 are respectively terrninated in a non-reflectiveload 71-- and'theradia'tor'595 The phase shifter'70 is substantially identical to the" phase shifter 28 and includes apair of-wav'e guidesections- 72'and;74 connected respectively to the secondary"wave-- guide sections 66 and68 ofthe'respective hybrid'couplersland 62. As in the phase shifter 28; thew/ave guide sections 72 and 74 are-terminated in short circuiting plungers 76 and 78 adjustably supported by rod's 80 aud 82' joined by a yoke 87. The yoke 87 and associatedplung'ers76 and 78-are adjustably positioned-by anticrometer screw arrangementcontrolled by a knob 86.*

The phase shifter 70 is modifiedby the provision'of" resonant cavities positioned in the'respective wave-guide sections 72 and 74 between the hybrid coupler andtht: short-circuiting plungers. The cavities are formed by inductive irises indicated at 88, 90, 92 and 94; spaced slightly less than a half length along therespective w'avefl guides to provide a structure exhibiting parallel resonance at the operating frequency of the system. Extending through the wave guide sections 72-and 74w'ithin the resonant cavities is a'U-shaped gas tube 95. See Fig; The ends of the gas tube are provided with electrodes which are connected to the pulser 12, the latter serving egesdeoe It will be seen that if the path length between the two hybrid couplers through the phase shifter 70 is equal to or is related according to'an integral ratio of wavelengths to the path length along the wave guide section 64, due to the two 90 phase shifts produced by the couplers 60 and 62, the portion of energy finally coupled back into the main section 64- lags by 180 the energy coupled directly along the main wave guide section 64.

Shims 96 may be'insertedin a joint'in the wave guide s'e'ctio'ns'72" and 74 to' adjust thepath length to obtain the required ratio of p'ath' lengths. This 180 phase shift produces'complete'cancellation between the direct energy wave and'the coupled energy wave in the wave guide section 34. However, the energy propagating directly down the main wave guide section 64 coupled by the hybrid coupler 62 into the secondary wave guide section 68 is in phase with the energy from the phase hift r? 70, providing" reinforcement; Thus With the to periodically ionize the gas tube and produce a glowdischarge therein. When the gas discharge tube is thus fired, the cavities are effectively detuned, providing a short-circuiting type mismatch substantially in the plane of the irises 88 and 92. By spacing the irises8 8"and- 92 substantially three quarters of a wavelength from-"the shorting" plungers 76 and 7 8, with firing of the gas tube 95, the'phas'e of energy coupled through the phase shifter 70, is shifted by a wavelength and a half. The operation of theswitch 32 is as follows: y

The'hybrid couplers 60 and 62 inherently introduced a 90 phase lag in the coupled wave 'relativ'e totheldirect" wave. Thus, incident energy from thejwave" guidese'ction 30 divides at the hybrid coupler'60, half the energy being coupled directly down thewa've guide section 64, and half'the" energy being coupled into the secondary" wave guide section 66. The coupled wavein the section 66 lags the direct wave in the section 64 by 90. The coupled wave passes through the phase shifter 101a the" secondary wave guide section '68 of the hybridcoupler' 62 where it is divided equally into two' portions, one portion being coupled ba'ck'into the main wave .guide" section 64 with an additional 90 phase lag. Similarly, the direct wave down the main" wave guideQsectionI64' divides in the directional coupler 62, withhalf the energy continuingon down the main w'a'v'e' guidefse'ction 34 and half the energy being coupled into the secondary wave guide section "68';

phase shifter providing an integral-ratio of path lengths in -te'rr'ns 'of wavelengths-for the direct and coupled waves frorn'the hybrid coupler 60,- theoutput at the antenna 59 is of the same magnitude as the-incident energy from thenvave guide section30;

If-the efiective path length'of the'coupled wave'through th'e'phase shifter 70 is'shi'fted by a half wavelength or integral multipl'e*the'reof,:then it'will be seen that cancellation takes place between the direct and coupled waves in -thef secondary wave guide section o'f coupler 62, with reinforcement taking place in'the'wave guide'section 34. No energy is'delivere'd to the antenna 59 but all is recirculated'in' the storage loop. Thus, it will be seen that -by proper setting of" the phase shifter 70; energy from'thesource 10'can be caused to recirculate in the closed loop path until the gas tube'is'fired. Firing of the ga's tube shifts the-phase'the required-amount to cause' th'e eiiergy to-be diverted from the closed loop path to the antenna 59. The output of the antenna then has an energy "content" determined by the energy stored in the closed loop before firingof 'the'tube 9 5 and'has a pulse time-duration deterin'ined'solely bythe propagation time around'the loop;

From'theabove description it will'be seen that the various objects of the invention have-b'een-achieved by a pulsing apparatus which 'is capable-ofbuilding up the power lei/elf of transmitted pulses der'ived from a source of moderate'power'.- The'pulses-can be made of extremely sh'ort'duration'and are notirifluenced in duration by the deioniz'a'tiontime of the gas tubeor'sirnilar factors.

The apparatus a'sdescribed can also be utilized as a duplex'er in a' radar system i by replacing the non-reflect ing load'71' by a radar receiver. 7 Received energy normallycancels out inthe closed loop path, with all the energy going to the termination 71.

Whilethe gas tube has been shown as being fired by an external signal derived from a pulsing circuit, the gas tube-can be' designed to be fired by the incident microw ve energy so that the sto'rage loop is discharged when-' everth'e power level reaches a' predetermined critical level:

Since'many changescould be madein the above construction and'many apparently widely different embodinients' of this invention could'be' made without departing' fi'orrithe'scope thereof, it is' intended that all matter contained in the above description or shown in the ac cempanying'drawings shall be interpreted as illustrative and not in a limiting sense;

What'i's claimed is: v

1.-Microwave pulsingi' apparatus comprising a directionall coupler having primary and secondary wave guide sections, a source of microwave energy coupled to the primary wave guide section, wave guidemean coupling together opposite ends of the secondary wave guide secam to form a closed lo'op conductive path, the closedloop path bcingan integral number jot-wavelengths long at f the frequency of the microwave source, and switchingmeans for periodically couplingout energy circulating in the closed loop path including first and second hybrid couplers each having primary and secondary wave guide sections, the respective primary wave guide sections being connected in series with said wave guidemeans as part of the closed loop'conductive path, a third hybrid coupler having a pair of wave guide sections connected respectively to the secondary wave guide sections of the first and second ;hybrid; couplers, each of the pair of wave guides of the third hybrid coupler being terminated in a short circuit, inductive iris means defining a parallel resonant cavity region in each of said pair of wave guide sections of said third hybrid coupler spaced an odd multiple of a quarter wavelenth from the short circuit terminations, the cavities being resonant .at the operating frequency of the source, and glow discharge means positioned in the cavity regions for detuning the cavities when said glow discharge means is fired.

2. Microwave pulsing apparatus comprising a directional coupler having primary and secondary wave guide sections, a source of microwave energy coupled to the primary wave guide section, wave guide means coupling together opposite ends of the secondary wave guide section to form a closed loop conductive path, the closed loop path being an integral number of wavelengths long at the frequency ofthe' microwave source, arid switching means for periodically coupling outenergy circulating in. the closed loop path comprising first and second hybrid couplers each having primary and secondary wave guide" sections, the respective primary wave guide sections being connected in series with said wave guide means as part of the closed loop conductive path, and phase shifting means for intercoupling the respective secondary wave guidesections of the first and second hybrid couplers, said phase shifting means including means for occasionally shifting the phase of the energy flowing through the intercoupled secondary waveguide sections of the first and second hybrid couplers. a

i 3, Microwave pulsing apparatus comprising a microwave source, a wave guide loop forming a continuous closed conductive path, directional coupling means for coupling microwave energy into the loop in one direction of propagation from thesource, the loop being an integral number of wavelengths long at the frequency'of the source, power divider means connected in said loop for coupling out half the-incident power, four-terminal hybrid coupling means connected in the loop by two terminals of said hybrid coupling means, means coupling the third terminal of said hybrid coupling means to the output of the power dividing means, said coupling means in- .cluding means for abruptly shifting the phase of the energy coupled to the third terminal of the hybrid coupling means by a half Wavelength, and utilization means coupled to the fourth terminal of the hybrid coupling means. 7

4. Microwave pulsing apparatus comprising a microwave source, a wave guide loop forming a continuous closed conductive path, directional coupling means for coupling microwave energy into the loop in one direction of propagation from the source, the loop being an integral number of wavelengths long at the frequency of the source, microwave switching means coupled in said wave guide loop, utilization means coupled to said switching means, and means periodically actuating said switcha ing means for opening the loop and diverting the energy stored in the loop to the utilization means.

5. Apparatus comprising a directional coupler having primary and secondary waveguide sections, a source of microwave energy coupled to the primary waveguide section, waveguide means coupling together opposite ends of the secondary waveguide section. to form a closed loop conductive path, the closed loop path being an integral number of wavelengths long at the frequency of the microwave source, switching means having at least a'low and a high coetficient'of coupling for coupling out energy circulating in the closed loop path, and means for periodically actuating said switching means whereby to change the coefiicient of coupling of said switching means from said low coefiicient of coupling to said highcoeflicient of coupling to vary the level of the energy circulating in the closed loop path. 

